1. Field of the Invention
The invention relates to methods of treatment for preservation and healing of corneal tissue. Compositions for such treatment comprise pharmaceutically acceptable compositions of hepatocyte and keratinocyte growth factors singly and in combination.
2. Description of Related Art
Corneal wound healing and the many factors which may promote or prevent it have been of concern to both clinicians and researchers. Opthomologists are frequently confronted with corneal dystrophies and problematic injuries that result in persistent and recurrent epithelial erosion, often with permanent endothelial loss. Many attempts have been made to use growth factors to stimulate healing of the corneal epithelium and endothelium following injury or surgery. However, only a limited number of approaches are currently available for treating patients who fail to heal epithelial injuries adequately.
Epidermal growth factor (EGF) is one substance that has been investigated as a means to stimulate the healing of corneal epithelium and endothelium following injury or surgery. This factor have also been tested as storage media for corneal preservation in attempts to improve the viability of corneal endothelial cells following corneal storage. The majority of the available in vitro and in vivo studies on corneal tissue have been performed with epidermal growth factor (EGF).
Many attempts have been made to use EGF to stimulate the healing of the corneal epithelium and endothelium following injury or surgery. Similarly, EGF has been added to storage media used for corneal preservation in attempts to improve the viability of corneal epithelial and endothelial cells following corneal storage.
Epidermal growth factor has been shown to stimulate the proliferation of bovine corneal epithelial cells in vitro (Gospodarowicz, et al., 1977). Similarly, in vivo animal studies have shown that epidermal growth factor stimulates corneal epithelial wound healing in the rabbit (Soong, et al., 1989) and rat (Brazzell, et al., 1991); Kitazawa, et al., 1990); Chung and Fagerholm, 1989; Reim, et al., 1988) after superficial epithelial wounding, keratectomy wounds of the anterior corneal surface, and corneal alkali burns. In two of these studies, however, there was increased vascularization (Chung and Fagerholm, 1989) and increased inflammatory response (Reim, et al., 1988) in the epidermal growth factor treated corneas compared with the control corneas. One randomized prospective trial of epidermal growth factor for the treatment of epithelial wounds (Kandarakis, et al., (1984)) demonstrated no difference between epidermal growth factor and vehicle alone in the rate of corneal epithelial wound healing after penetrating keratoplasty. Thus, despite the fact that epidermal growth factor has been available for over a decade, in vivo randomized trials have not demonstrated that epidermal growth factor stimulates corneal epithelial wound healing compared with controls.
The background for the use of EGF for the corneal endothelium is very similar. EGF stimulates in vitro proliferation or migration of bovine endothelium (Gospodarowicz, et al., 1977; Junquero, et al., 1990 and rabbit Raymond, et al., 1986; Joyce, et al., 1989). Similarly, epidermal growth factor stimulates the in vitro proliferation of human corneal endothelial cells (Nayak, et al., 1984). The use of epidermal growth factor in corneal preservation and intraocular use during eye surgery have been proposed (Neufeld, A. H., 1991). In two independent studies, however, epidermal growth factor did not stimulate the healing of cat corneal endothelium in vivo when epidermal growth factor was injected into the eye after cold-induced injury (Rich, et al., 1991; Brogdon, et al., 1989). A disappointing result was recently shown in a masked, randomized, prospective, multicenter trial in which paired corneas from the same donor were preserved in identical corneal preservation media with or without epidermal growth factor. There was no difference in the corneal endothelial cell counts between the epidermal growth factor and control groups at one or two years of follow-up (Lass, unpublished data).
The functional status of the endothelium and sustained corneal deturgescence after corneal preservation are also clinically important and are primary goals in the development of corneal storage media. Desirable storage characteristics include the extension of corneal preservation time, enhancement of corneal wound healing, and the reduction of normal progressive loss of endothelial cells post keratoplasty. In preserving corneas for transplants, for example, it is important that the endothelial cells remain viable and metabolically active and able to change to a mitotically active state after implantation.
The negative results obtained with EGF-stimulated corneal epithelial wound healing and corneal endothelial preservation in randomized prospective trials highlight a lack of other more effective agents to stimulate corneal epithelial and endothelial proliferation and preservation after wounding or during corneal preservation.
There is therefore a need to develop compositions that have a beneficial effect on corneal wound healing. While some studies indicate that EGF may have a beneficial effect in promoting epithelial cell proliferation, its effect on endothelial cell viability is problematic. Healing and preservation of both epithelial and endothelial cells is important, particularly the latter, because endothelial cell viability and function is fundamentally important in maintaining corneal clarity and vision during the aging process as well as after disease, surgery, or laser treatments. At present, only a limited number of approaches are available for treating patients who fail to heal either epithelial or deep wound injuries involving endothelial cell structure.